In the manufacture of semiconductor devices and other products, ion implantation systems are used to impart impurities, known as dopant elements, into semiconductor wafers, display panels, or other work pieces. Typical ion implantation systems or ion implanters treat a work piece with an ion beam in order to produce n- or p-type doped regions, or to form passivation layers in the work piece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material. Typically, dopant atoms or molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and implanted into a wafer. The dopant ions physically bombard and enter the surface of the wafer, and subsequently come to rest below the surface.
A typical ion implantation system is generally a collection of sophisticated subsystems, wherein each subsystem performs a specific action on the dopant ions. Dopant elements can be introduced in gas form (e.g., a process gas) or in a solid form that is subsequently vaporized, wherein the dopant elements are positioned inside an ionization chamber and ionized by a suitable ionization process. For example, the ionization chamber is maintained at a low pressure (e.g., a vacuum), wherein a filament is located within the chamber and heated to a point where electrons are created from the filament source. Negatively-charged electrons from the filament source are then attracted to an oppositely-charged anode within the chamber, wherein during the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a plurality of positively charged ions from the source elements. The positively charged ions are subsequently “extracted” from the chamber through an extraction slit via an extraction electrode, wherein the ions are generally directed along an ion beam path toward the wafer.
Typically, a single ion implantation system is utilized to implant several differing dopant ion species into respective batches of wafers, wherein a change in species (e.g., a change from a first species or process gas to a second species or process gas) is necessitated in order to perform the specific ion implantations. One typical change in species is a change from a boron-containing process gas (which produces a p-type implant) to a phosphorus-containing process gas (which produces an n-type implant). One drawback to using a single ion implantation system for implanting various species of ions, however, is that such a change in process species can be quite time consuming, since ions from the first process gas are typically deposited onto internal walls of the ionization chamber, and such deposited materials can adversely affect subsequent implantations using other ion species. For example, upon changing from the first species to the second species, deposited ions of the first species that are attached to the internal walls of the ionization chamber are typically sputtered off by ions of the second species and subsequently exit the chamber through the extraction slit, thus contaminating the desired second species ion beam with ions from the first species. Furthermore, the sputtered first species can affect the ionization of the second species, and as a result, the extracted second species will typically require a substantially long amount of time to stabilize. Conventionally, for some specific species transitions, such as a transition from boron species to phosphorus species, in order to clear the ionization chamber of the previous species, the system is “transitioned” for a period on the order of thirty minutes or longer, wherein the desired species is used to clear the chamber of the previous species. Accordingly, at the end of transition period, ions of the previous species are generally insignificant in the resultant ion beam.
Long transition periods, however, can adversely affect the ion implantation process. For example, long transition times can affect auto-tune times for the implanter, as well as the stability and productivity of the ion implanter. Also, during the transition period, energy and process species are generally wasted while the system purges the previous species from the ionization chamber. Accordingly, a need currently exists for a more efficient ion implantation system and apparatus, wherein a speed in changing from one species to another can be significantly increased.